FPSIM fixed; 211bsd runs on systems without FPP

Some time ago I looked into running 2.11bsd on systems without
floating point unit. The release notes state that this is untested
and unsupported, and indeed it didn't work.

Robin Birch some time ago fixed part of the issues, see patch 434,
but still the kernel paniced when the very first program was started.
I managed to localize and fix the problem in sys/pdp/mch_fpsim.s.
Steven Schultz right away issued a patch

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